The natural human heart and accompanying circulatory system are critical components of the human body and systematically provide the needed nutrients and oxygen for operation of the body. As such, the proper operation of the circulatory system, and particularly, the proper operation of the heart, are critical in the life, health and well-being of a person. A physical ailment or condition which compromises the normal and healthy operation of the heart can therefore be particularly critical and may result in a condition which must be medically remedied.
More specifically, the natural heart, or rather the cardiac tissue of the heart, can degrade for various reasons to a point where the heart can no longer provide sufficient circulation of blood for maintaining the health of a patient at a desirable level. In fact, the heart may degrade to the point of failure and thereby may not even be able to sustain life. To address the problem of a failing natural heart, solutions are offered to provide ways in which circulation of blood might be maintained. Some solutions involve replacing the heart. Other solutions are directed to maintaining operation of the existing heart.
One such solution has been to replace the existing natural heart in a patient with an artificial heart or a ventricular assist device. In using artificial hearts and/or assist devices, a particular problem stems from the fact that the materials used for the interior lining of the chambers of an artificial heart are in direct contact with the circulating blood. Such contact may enhance undesirable clotting of the blood, may cause a build-up of calcium, or may otherwise inhibit the blood's normal function. As a result, thromboembolism and hemolysis may occur. Additionally, the lining of an artificial heart or a ventricular assist device can crack, which inhibits performance, even when the crack is at a microscopic level. Moreover, these devices must be powered by a power source which may be cumbersome and/or external to the body. Such drawbacks have limited the use of artificial heart and assist devices to applications having too brief of a time period to provide a real lasting health benefit to the patient.
An alternative procedure also involves replacement of the heart, but includes a transplant of a natural heart from another human or animal into the patient. The transplant procedure requires removing an existing organ (i.e. the natural heart) from the patient for substitution with another organ (i.e. another natural heart) from another human, or potentially, from an animal. Before replacing an existing organ with another, the substitute organ must be “matched” to the recipient, which can be, at best, difficult, time consuming, and expensive to accomplish. Furthermore, even if the transplanted organ matches the recipient, a risk exists that the recipient's body will still reject the transplanted organ and attack it as a foreign object. Moreover, the number of potential donor hearts is far less than the number of patients in need of a natural heart transplant. Although use of animal hearts would lessen the problem of having fewer donors than recipients, there is an enhanced concern with respect to the rejection of the animal heart.
Rather than replacing the patient's heart, other solutions attempt to continue to use the existing heart and associated tissue. In one such solution, attempts have been made to wrap skeletal muscle tissue around the natural heart to use as an auxiliary contraction mechanism so that the heart may pump. As currently used, skeletal muscle cannot alone typically provide sufficient and sustained pumping power for maintaining circulation of blood through the circulatory system of the body. This is especially true for those patients with severe heart failure.
Another system developed for use with an existing heart for sustaining the circulatory function and pumping action of the heart, is an external bypass system, such as a cardiopulmonary (heart-lung) machine. Typically, bypass systems of this type are complex and large, and, as such, are limited to short term use, such as in an operating room during surgery, or when maintaining the circulation of a patient while awaiting receipt of a transplant heart. The size and complexity effectively prohibit use of bypass systems as a long term solution, as they are rarely portable devices. Furthermore, long term use of a heart-lung machine can damage the blood cells and blood borne products, resulting in post surgical complications such as bleeding, thromboembolism function, and increased risk of infection.
Still another solution for maintaining the existing natural heart as the pumping device involves enveloping a substantial portion of the natural heart, such as the entire left and right ventricles, with a pumping device for rhythmic compression. That is, the exterior wall surfaces of the heart are contacted and the heart walls are compressed to change the volume of the heart and thereby pump blood out of the chambers. Although somewhat effective as a short term treatment, the existing pumping devices have not been suitable for long term use.
Typically, with such compression devices, heart walls are concentrically compressed. A vacuum pressure is then needed to overcome cardiac tissue/wall stiffness, so that the compressed heart chambers can return to their original volume and refill with blood. This “active filling” of the chambers with blood limits the ability of the pumping device to respond to the need for adjustments in the blood volume pumped through the natural heart, and can adversely affect the circulation of blood to the coronary arteries. Furthermore, natural heart valves, between the chambers of the heart and leaching into and out of the heart, are quite sensitive to wall distortion and annular distortion. The compressive movement patterns that reduce a chamber's volume and distort the heart walls may not necessarily facilitate valve closure (which can lead to valve leakage).
Therefore, mechanical pumping of the heart, such as through mechanical compression or distortion of the ventricles, must address these issues and concerns in order to establish the efficacy of long term mechanical or mechanically-assisted pumping. Specifically, the ventricles must rapidly and passively refill at low physiologic pressures, and the valve functions must be physiologically adequate. The myocardial blood flow of the heart also must not be impaired by the mechanical device. Still further, the left and right ventricle pressure independence must be maintained within the heart.
The present invention addresses the issues of heart wall stiffness and the need for active refilling by assisting in the bending (i.e., indenting, flattening, twisting, etc.) of the heart walls, rather than concentrically compressing the heart walls. Because of the mechanics of deformation in hearts having proportions typical in heart failure (specifically, wall thickness/chamber radius ratios), the deformation from bending and the subsequent refilling of the heart requires significantly less energy than would the re-stretching of a wall that has been shortened to change the chamber volume a similar amount. The present invention facilitates such desirable heart wall bending and specifically protects the heart wall during such bending.
Another major obstacle with long term use of such pumping devices is the deleterious effect of forceful contact of different parts of the living internal heart surface (endocardium), one against another, due to lack of precise control of wall actuation. In certain cases, this coaptation of endocardium tissue is probably necessary for a device that encompasses both ventricles to produce independent output pressures from the left and right ventricles. However, it can compromise the integrity of the living endothelium.
Mechanical ventricular wall actuation has shown promise, despite the issues noted above. As such, devices have been invented for mechanically assisting the pumping function of the heart, and specifically for externally actuating a heart wall, such as a ventricular wall, to assist in such pumping functions.
Specifically, U.S. Pat. No. 5,957,977, which is incorporated herein by reference in its entirety, discloses an actuation device for the natural heart utilizing internal and external support structures. That patent provides an internal and external framework mounted internally and externally with respect to the natural heart, and an actuator or activator mounted to the framework for providing cyclical forces to deform one or more walls of the heart, such as the left ventricular wall. The invention of U.S. patent application Ser. No. 09/850,554, which is also incorporated herein by reference in its entirety, further adds to the art of U.S. Pat. No. 5,957,977 and specifically sets forth various embodiments of activators or actuator devices which are suitable for deforming the heart walls and supplementing and/or providing the pumping function for the natural heart.
When heart wall actuation systems like those noted above are utilized, the heart wall is actuated by being indented and/or deformed proximate a chamber of the heart to change the volume of the chamber. When actuated or indented in such a way, a heart wall, or at least portions of the wall may have a tendency to take on shapes which are not desirable from a physical standpoint. More specifically, the heart walls may have a tendency to become overly distended, or take on sharp curvatures, in certain areas based upon the indentation of those walls in other areas. Such unnatural shaping of the heart tissue may be damaging to the tissue. Therefore, when utilizing a heart wall actuation system, one issue to be addressed is the shape of the walls when the system is actuated, and the variance of that shape from the natural shape that the heart would assume when pumping normally.
It is therefore an objective of the present invention to assist in the operation of heart wall actuation systems with the natural heart.
It is a further objective to reduce and prevent unnatural distortion of the heart and its components during activation with a heart wall actuation system.
It is still another objective of the present invention to provide long term actuation and assistance for the heart by reducing unnatural stress on the heart during such actuation.
These objectives and other objectives and advantages of the present invention will be set forth and will become more apparent in the description of the invention below.